In recent years, as a solution to problems such as global warming due to an increase in carbon dioxide associated with the consumption of fossil fuels, clean renewable energy that does not emit carbon dioxide has attracted attention instead of the fossil fuels.
Solar energy, which is one of the renewable energy, has no worry of exhaustion. The use of the solar energy can contribute to the reduction in greenhouse gases. Under such circumstances, an energy system in which primary energy is sought from solar light and secondary energy is supported by hydrogen is one of the ideal clean energy systems. Establishment of such an energy system is an urgent matter.
As one method of converting solar energy into chemical energy, for example, the use of ceramic members such as ceria (CeO2) as a reaction system carrier has been developed. This method utilizes a two-step hydrolysis reactions occurring in the reaction system carrier (for example, refer to Patent Literature 1).
Specifically, first of all, in a first step, the ceramic member as the reaction system carrier is heated to 1400° C. to 1800° C. using solar energy. In this first step, oxygen is generated by the reduction of the ceramic member.
Subsequently, in a second step, the reduced ceramic member is cooled to 300° C. to 1200° C. In this second step, the ceramic member is reacted with water. In this reaction, the reduced ceramic member is oxidized to generate hydrogen.